Очень странное поведение программы

//Made by SharpSided
//Date *date*
 
package com.sharpsided.main;
 
public class Main {
    
    public static void main (String[] args){
        PaintToolGUI window = new PaintToolGUI();
        window.drawGUI();
        window.setVisible(true);
    }
}

//Made by SharpSided
//Date *date*
 
package com.sharpsided.main;
 
import java.awt.*;
import java.awt.event.MouseEvent;
import java.awt.event.MouseListener;
 
import javax.swing.*;
import javax.swing.event.ChangeEvent;
import javax.swing.event.ChangeListener;
 
@SuppressWarnings("serial")
public class PaintToolGUI extends JFrame{
    
    //Loads
    private Dimension windowSize = new Dimension(770, 500);
    private DrawPanel drawPanel = new DrawPanel();
    
    //Component loads
    private JPanel mainPanel = new JPanel();
    private JToolBar toolBar = new JToolBar();
    private JButton brushButton = new JButton();
    private JButton eraserButton = new JButton();
    private JButton sphereButton = new JButton();
    private JButton boxButton = new JButton();
    private JButton sphericButton = new JButton();
    private JSlider colorSlider1 = new JSlider(JSlider.HORIZONTAL, 0, 255, 0);
    private JSlider colorSlider2 = new JSlider(JSlider.HORIZONTAL, 0, 255, 0);
    
    //Image loads
    private ImageIcon brushIcon = new ImageIcon("images/brushTool.png");
    private ImageIcon sphericIcon = new ImageIcon("images/sphericBox.png");
    private ImageIcon boxIcon = new ImageIcon("images/boxTool.png");
    private ImageIcon sphereIcon = new ImageIcon("images/sphereTool.png");
    private ImageIcon eraserIcon = new ImageIcon("images/eraserTool.png");
    
    //Listener loads
    private MListener mouseListener = new MListener();
    private SlideListener slideListener = new SlideListener();
    
    //Constructor
    public PaintToolGUI(){
        super("Paint-Tool by_SharpSided");
        setSize(windowSize);
        setDefaultCloseOperation(JFrame.EXIT_ON_CLOSE);
        setLocationRelativeTo(null);
    }
    
    //GUI
    public void drawGUI(){
        mainPanel.setLayout(new BorderLayout());
        
        brushButton.setIcon(brushIcon);
        eraserButton.setIcon(eraserIcon);
        sphereButton.setIcon(sphereIcon);
        sphericButton.setIcon(sphericIcon);
        boxButton.setIcon(boxIcon);
        
        colorSlider1.addChangeListener(slideListener);
        setColorSlider(colorSlider1);
        setColorSlider(colorSlider2);
        
        toolBar.setFloatable(false);
        toolBar.add(brushButton);
        toolBar.add(eraserButton);
        toolBar.add(sphereButton);
        toolBar.add(sphericButton);
        toolBar.add(boxButton);
        toolBar.add(colorSlider1);
        toolBar.add(colorSlider2);
        
        add(drawPanel, BorderLayout.CENTER);
        add(toolBar, BorderLayout.SOUTH);
        
        drawPanel.addMouseListener(mouseListener);
    }
    
    void setColorSlider(JSlider slider){        
        slider.setMajorTickSpacing(50);
        slider.setMinorTickSpacing(10);
        slider.setPaintTicks(true);
        slider.setPaintLabels(true);
    }
    
    //Draw panel
    class DrawPanel extends JPanel{
            
        Graphics draw;
        
        public void paintComponent(Graphics g){
            
            draw = g;
            
            draw.setColor(Color.black);
            draw.fillOval(50, 50, 100, 100);
        }
        
        public void setColor(Color col){
            draw.setColor(col);
            drawPanel.repaint();
        }
    }
    
    class MListener implements MouseListener{
        
        public void mouseClicked(MouseEvent event){ 
            
        }
        
        public void mouseEntered(MouseEvent event){ 
            
        }
        
        public void mouseExited(MouseEvent event){ 
            
        }
        
        public void mousePressed(MouseEvent event){
            
        }
        
        public void mouseReleased(MouseEvent event){ 
            
        }
    }
    
    class SlideListener implements ChangeListener {
        public void stateChanged(ChangeEvent event){
            JSlider source = (JSlider) event.getSource();
            if(source == colorSlider1){
                int curentState = colorSlider1.getValue();
                Color sliderBack = new Color(curentState, curentState, curentState);
                drawPanel.setColor(sliderBack);
            }
        }
    }
}

    class DrawPanel extends JPanel {
        Color c = Color.BLACK;
 
        public void paintComponent(Graphics g) {
            super.paintComponent(g);
            g.setColor(c);
            g.fillOval(10, 0, 100, 100);
        }
 
        public void setColor(Color col) {
            c = col;
            repaint();
        }
    }